DE2520783A1 - LOW PRESSURE CASTING DEVICE - Google Patents

Description

The invention relates to a low-pressure casting device a mold that is at the bottom with a compression relaxation s chamber is in communication, which in turn is connected via a dip tube to a sealed enclosure

/ And ordered crucible is connected / a first and a second, at its lower end communicating sub-chambers, of which the second in its upper Part is provided with an outlet port which leads to a source of pressurized, opposite that in the crucible The casting material contained indifferent gas is connected, with a gate valve between this and the outlet nozzle and a gas flow regulator interposed, and wherein the sealed enclosure is provided with a pressure supply port is provided, which is connected to a compressed air source with the interposition of a gate valve.

There are so-called low-pressure casting processes are known in which on the free surface of a casting material that is in the liquid state in a crucible placed in a sealed enclosure, for example in a sealed furnace is located, a gas pressure is applied. The casting material can be a metal, an alloy or a synthetic resin.

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The overpressure generated in the tight enclosure causes the liquid casting material to rise in a dip tube, which is connected to a mold at its upper end. Holes are drilled in these for the escape of gas. In the dip tube is inserted between the crucible and the casting mold, a compression-relaxation chamber, which is a first and a second sub-chamber communicating with one another. During the pressurization phase of the tight enclosure, the second sub-chamber forms a gas bell.

After at least partial solidification of the liquid casting material In the casting mold, the gas pressures in the tight enclosure and in the second sub-chamber are equalized, after which atmospheric pressure is restored in these two spaces so that the casting material that has not solidified can fall back into the crucible.

A casting device for carrying out this method in particular when casting hollow parts is described in French patent specification 71 28 190.

In such a device it is provided that for pressurization the tight enclosure compressed air or a gas that is indifferent to the casting material can be used can.

However, it has been found, especially when casting metals and alloys using the low-pressure casting process, that practically always oxidation phenomena occur. This often strong oxidation in the liquid metal occurs when the pressure is released to allow the non-solidified metal to flow back into the dip tube and then back into the crucible.

In fact, the interface between the solidified part and the liquid part is never smooth. In a pulpy state Parts located loosen, oxidize and collect in the

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Immersion tube on the surface of the liquid. Each time the casting mold is filled, oxides accumulate and enter the casting be transported and can reduce or change its quality.

Such phenomena can also occur when the pressurized gas used to pressurize the device is an indifferent gas.

The invention is based on the object of avoiding the formation of oxides, of removing oxides formed accidentally and to facilitate degassing in the device, which has not been possible up to now.

The invention relates to a low-pressure casting device, in which the enclosure surrounding the crucible, depending on If required, it can either be connected to a compressed air source or can be tightly sealed or connected to the atmosphere, and in which the second sub-chamber of the compression-relaxation chamber is provided in its upper part with an outlet port, which as required to a source for pressurized inert gas can be connected, with devices for the interruption in this outlet connection the gas supply and for regulating the gas flow rate are installed.

The invention is also directed to an apparatus of this type directed, which has an automatic feed and metering device for the compressed air and the inert gas, too which includes a swiveling container in which the compressed air or the indifferent gas are included.

According to the invention, the above-mentioned sealed enclosure surrounding the crucible is pressurized with compressed air, and the second sub-chamber of said compression-release chamber is based on requirements and when controlled

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the flow rate and the pressure is supplied with a gas that is indifferent to the casting material.

Thanks to this division of the tasks to be performed by the gases, those caused by the oxidation can be eliminated Avoid disadvantages. This result is achieved by using only a small and metered amount of inert compressed gas, which can be nitrogen or argon, for example, as the main pressure generation in the device with Compressed air is made.

In an embodiment according to the invention, the inert gas with a small (flow) amount is used before each casting process introduced into the second sub-chamber. The second sub-chamber filled with inert gas is then sealed off and said inclusion is pressurized with compressed air. After at least partially solidified Indifferent gas is again introduced into the second sub-chamber and said inclusion is released with the atmosphere connected, with the supply of inert gas during the return of the non-solidified casting material into the crucible is maintained in the second sub-chamber.

According to an advantageous embodiment of the invention, at the end of a casting process and after the whole is not solidified casting material has run back into the crucible, temporarily the supply of the inert gas into the second subchamber continued, this inert gas escaping through the immersion tube and the crucible to the immersion tube to free of impurities and to bubble through the liquid casting material before it ai the free surface of the Casting material emerges.

The invention is particularly with low pressure casting apparatus applicable as described in said French patent.

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The automatic feed device for compressed air and indifferent Gas according to the invention has a very simple structure and prevents any exchange between the two areas "Compressed air" and "indifferent gas" and enables an exact and constant dosage of the indifferent purging gases, which results in an improved metallurgical quality of the castings.

The invention is illustrated below with the aid of schematic drawings of several exemplary embodiments with further details explained. In the drawing shows:

1 shows a section through a low-pressure casting device to explain the method according to the invention,

Pig. FIG. 2 shows a section through part of a preferred embodiment of a casting device according to FIG Invention,

3 shows a further section through the casting device according to FIG. 2 to explain the processes in Deoxidizing and degassing,

Fig. 4 is a plan view, partially in section, of a low-pressure casting device according to the invention applicable automatic feed device for inert gas, and

5 and 6 are top views, partly in section, of the one in the feed device according to FIG. 4 as a metering device used cylinders in two different positions.

As an example to explain the method according to the invention, FIG. 1 shows a low-pressure casting device of the type shown in FIG. aforementioned French patent described genus.

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It suffices to point out that the casting device has a tight enclosure 2, for example an oven, in which a crucible 4 is arranged. This contains the casting material 6 in the liquid state, for example a metal or a light metal alloy. A vertically or obliquely arranged dip tube 8 is inserted into the liquid metal immersed, which is connected to a casting mold 10 at its upper end. Between the dip tube 8 and the casting mold 10 a compression-relaxation chamber 12 is arranged. The casting mold 10 is provided with a gas discharge device 14 at its upper end.

The compression-relaxation chamber 12 is composed of a first sub-chamber 16 and a second sub-chamber 18 together, which at their lower part via a passage 20 with one another stay in contact. The second sub-chamber 18 forms a gas bell which can enclose a "compressed gas cushion" 22, and is provided with an outlet port 24 at its upper part.

The inclusion 2 is in turn with a pressure feed clip Mistake.

In the outlet port 24 are a gate valve 28 and a Built-in flow limiter or flow regulator 30. The other end 32 of the outlet port 24 is connected to one in Pig. Source designated by IT for a source that is indifferent to the casting material, for example to an aluminum alloy Gas connected. For example, nitrogen, argon or any other gas that contains the same can be used Has properties and with which a non-oxidizing atmosphere is created in the upper area of the liquid metal leaves.

In the pressure supply nozzle 26 is a gate valve, in the example shown a directional valve 34 with three positions built in, with which the inclusion 2 either as required

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to a compressed air source designated by A "in FIG. 1 or connect to a pipeline 36 leading into the open air or can be sealed tightly.

In the first operating phase of the method, after the casting mold 10 has been ejected from the previously produced casting was closed again, the directional control valve 34 closed, the inclusion 2 is under atmospheric pressure, and the Gate valve 28 is opened, the flow regulator a small amount, for example of the order of 1 l / min, inert gas lets through, with which the feed part is flushed under low pressure.

In the second working phase of the process, inert gas is fed in by closing the gate valve interrupted. By opening the directional control valve 34, corresponding to the position shown in FIG. 1, pressurization takes place the casting mold 10, the compressed air source A is connected. The liquid metal rises in the dip tube 8 high into the Compression-relaxation chamber 12 and into the casting mold 10. In the second sub-chamber 18, the liquid metal presses a cushion 22 composed of inert gas.

During the complete or partial solidification of the casting, depending on whether solid or hollow parts are produced the directional control valve 34 is closed again in order to maintain the filling pressure.

In the third working phase of the process, ie after the casting has completely or partially solidified and shortly before the pressure in enclosure 2 is again reduced to atmospheric pressure, the gate valve 28 is opened again in order to introduce a small amount of inert gas into the sub-chamber 18, until the liquid in this sub-chamber 18 has reached a level at which the inert gas can escape into the upper part of the sub-chamber 16. This operating state of the casting device is shown in Fig. 2, which shows part of a preferred embodiment of the invention.

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After the connection to the atmosphere is made again with the directional control valve 34, while the metal is in the Immersion tube 8 runs back completely, the supply of indifferent Gas in outlet connection 24 throttled to a very small flow rate until the pressure drop has ended it is possible in the fourth phase of the process to remove the casting and to continue with the next step in the Maintaining a neutral or indifferent atmosphere.

As can be seen in connection with FIG the method and the device according to the invention also for degassing and deoxidation, in particular use to remove the oxides that may have accumulated in the dip tube 8.

Pig. 2 and 3 show a preferred embodiment of a casting device for carrying out the method according to FIG Invention.

The essential components have the same reference numerals as the corresponding parts of the example according to FIG. 1. In the embodiment shown in FIGS. 2 and 3, the immersion tube 8 is not arranged obliquely, but vertically and the compression-release chamber 12 has a special configuration.

The compression relaxation chamber 12 of the example shown has a shape that is rotationally symmetrical to a vertical axis and can be composed of two parts 38 and 40 be substantially frustoconical, as individual parts assembled or cast in one piece and designed so that the first sub-chamber 16 of the compression-relaxation chamber 12 is located in the center thereof, while the second sub-chamber 18 extends annularly around the first sub-chamber 16 .

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If the metal, or more generally the casting material, during the second working phase in the compression-relaxation chamber 12 a in Pig. 2 reached level 42 drawn in with dashed lines, that shown in FIG Molding material level corresponds, is in a tight upper part of the annular bead-shaped volume of the second sub-chamber 18 a certain mass of indifferent gas included, which forms the pressure pad 22.

As soon as the liquid metal reaches the level 42, the two sub-chambers 16 and 18 are inserted into the liquid through one Metal immersing annular partition 44 separated from one another.

Fig. 2 shows precisely the third working phase of the method, i.e. that phase in which after complete or partial Solidification of a casting 46 through the outlet 24 a small amount of inert gas is introduced until the liquid is one level in the annular chamber space reached, in which the indifferent gas, as indicated by arrows 50, in the upper central area of the device can escape.

In Fig. 2 and 3, a safety device is also shown, which consists of two electrodes or contact pieces is formed, which are short-circuited when the metal is above the level provided in the sub-chamber 18 increases, for example in the case of poor sealing of this sub-chamber 18 as a result of a leak on or in front of the Outlet connection 24. The safety device 52 then automatically interrupts the pressurization of the enclosure 2.

Fig. 3 shows in particular the possibilities of degassing and deoxidation, as they are a device of the invention. If such a treatment is to be carried out, it is sufficient to connect the nozzle to the casting mold to make tight with a plug 54 and that over

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the outlet port 24 supplied inert gas, for example nitrogen, to put under excess pressure so that it is in the liquid melt bubbled through. The inclusion 2 is through an opening 56, for example the filling opening can be, or connected to the open air by switching the directional control valve 34 (Fig. 1) accordingly. The oxides that are in the Immersion tube 8 may have accumulated, are transported to the surface of the melt, so can no longer with each Filling of the casting mold 10 are entrained in the casting, and the liquid metal experiences a vigorous degassing.

Fig. 4 shows a metering feed device for inert gas to a low-pressure casting device according to the invention. This device is connected to a casting device designed identically to the casting device shown in FIGS. 2 and 3 connectable. For this reason, only that part of the inclusion 2 is drawn from which the pressure supply nozzle 26 extends, and of the compression-relaxation chamber 12 - only the part to which the outlet connection 24 is connected.

The feed device includes a sealed cylinder 58, which is pivotable about its support axis 60 and its interior through a diametrically extending partition wall 62 is divided, which has a passage 64 in its lower part. This Cylinder 58 is half oil or any filled with another liquid that is non-volatile, very stable and inert to the selected gas. In the upper part of the respective space V .. or Vp opens in each case an inlet 66 and 68. These are extended with very flexible hoses 70 and 72 to the pivot center. The cylinder 58 is provided with a light ballast weight 74 which acts as a return device and the cylinder 58 normally holds in the position shown in FIG.

The outlet nozzle 24, which opens in the upper region of the compression-relaxation chamber, is connected to the _{inlet 66 connected to the space V 1} via a hose,

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the pivot "movements of the cylinder 58 about its support axis 60 not affected.

Between the cylinder 58 and the compression-release chamber 12, a gate valve 28 and a feed line for indifferent gas coming from a source N are interposed. The gas is metered with the flow regulator 30, which also acts as a pressure reducing valve.

The inlet 68 connected to the room Vp is also with a flexible line, connected to the pressure supply port 26 of the enclosure 2, which in turn is connected to the compressed air source A via the directional valve 34.

In the first working phase, which was described in more detail above, ie when the casting mold 10 was closed again after the last casting was ejected, the cylinder 58 is in a state of equilibrium, with its partition wall 62, as shown in FIG. 4, being vertical . The gate valve 28 is open. The flow regulator 30 allows a gas amount of, for example, 1 l / min through at low pressure in order to flush the feed part and to keep the inert gas in the space V ^ at atmospheric pressure. The directional control valve 34 is closed, the inclusion 2, like the space V ₂ , is under atmospheric pressure.

In the second work phase, as already described in more detail above, the directional control valve 34 is opened to to pressurize the enclosure 2, and the gate valve 28 is closed to the upper part 22 * of the second sub-chamber 18 to seal the compression-relaxation chamber 12 tightly and to form the pressure pad 22.

The increase in pressure in space V ₂ forces the liquid in cylinder 58 to the left and causes cylinder 58 to pivot, _{compressing the gas in space V 1} (FIG. 5).

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Under the effect of the pressure increase in space V ^ closes the flow regulator acting as a pressure reducing valve turns itself automatically. The balance of the angular position of the cylinder is achieved as soon as the mold 10 is filled and the pressures in the spaces V ^ and Vp are essentially equalized have, due to the fact that the ballast weight 74 is very light and just enough for the return to compensate for friction occurring in the initial equilibrium position.

At the end of the second working phase, the casting 46 is allowed to solidify completely or partially by adding closed directional control valve 34 maintains the filling pressure.

In the third working phase, the gate valve 28 is opened at the moment the pressure is reduced to atmospheric pressure, whereby the pressure in space V _{1 is} lowered and the solid part separates from the liquid part at the level of the lower part of the casting mold 10. The space V _{1 is} reduced under the effect of the limited expansion of the space V ₂ , since the directional control valve 34 is closed.

The cylinder 58 assumes the position shown in FIG. Thanks to this additional pivoting movement of the cylinder 58, as described above in connection with FIG. 2, automatically introduced a metered amount of inert gas.

In order to reduce the pressure in the enclosure 2, it is then sufficient to reconnect to the atmosphere via the directional control valve 34 produce, wherein the actuation of the directional control valve 34 can be time-controlled, for example 2 or 3 s after opening the gate valve 28, or by a limit switch 76 (Fig. 6) can be triggered at which the Cylinder 58 starts moving at the end of the pivoting movement.

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The atmosphere required for the separation is created and the liquid column sinks in the dip tube 8.

In the fourth working phase, the cylinder 58 goes back to its initial equilibrium position (Mg. 4) while the flow regulator 30 again lowers for flushing Lets the amount of inert gas through because it is no longer under counter pressure. The casting is then made from the Ejected mold. This is then closed again in an indifferent atmosphere and the work process begins all over again.

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Claims (6)

ο η ν; 1 »llieaeräruck-iiießvoinlchtujriß with a casting mold» those at the bottom ".'nuO with oilier" ^ OKiirosoioKO- ^ iitspamiusi ^ i ^ ^r \ „jxmt! T in Varbijadui ^ ?; stands, v / "live for your part via sin immersion tube rait hurried" in a tight -isssehluö arranged • crucible is connected uM eim erete and ciiHs sur ^ ito "a lower ", Ώάα oiteij ^ aidei ¹ · Xn connection etshenöe v? eist _f from öenen öio avmite i2i ihrsia upper "part with iUslaßötutiSön vex-BGhmi iot, äür im © ine Cuelle for] Prucli otohfindes, Gegcisilbor the ixa crucible al indifferent Goe ^ _t wherein uigeisckloseon eats öieeer and AuslaBstuteea an Ap IMD a Güsdnrchflußregler swieehörigeeciKiltet siisd "Urai wolsei the dense äinecfelxiß with eiiieis IIRUC * i; aullUiretuteöii eats the _f under 3wiseheiaäCh.jultuai £ oiiies ei" a DruckluftQii He ^ i ^ jgsechloßsen eats "approved" that it has a good food and odorless device for i ^ idifforentos gas iwa compressed air "which" viißchon "Jen Aiislaßetuts & n (24) and the BruökEuführstittuen (26) is in between. 2.! iederdrudfe-Gießvorrichtimis rxaeh jaoprueh 1 » pkaiiBSsiohnetf öriß aim tseXtmtt'-itiee looiervori'ichti «^ eiuien nit w ^ n ^ right leiipe mid us eeiixö Tt ^ ugaeh & e (60) freely sisterly with a riUsei ^ eit ^ filled gyliiider (5S) auiVn> lat _v the diiiioetral course through eäxe enäs Tr & mtstitmä, (62) in two i: üiieie (V ^ _f Vg- uxitertc- ilt i «t _t dio me through weiiigstsxia eJjae in the lower area äer ireKiH» ana. (62) also formed passage ) with the people in connection with each other , whereby the upper part is in its upper part ; - «Γ - 46 390 / sr the second space (Vp) in its upper part to the pressure supply nozzle (26) is connected. 3. Low pressure casting device according to claim 2, characterized characterized in that the first space (V ^) with the outlet connection (24) is connected via a flexible hose (70) between the gate valve (28) and the gas flow regulator (30), which is interposed between the source (N) for inert gas and the outlet connection (24) are connected. 4. Low-pressure casting device according to claim 2 or 3 _f, characterized in that the second space (V ") is connected to the pressure feed connection (26) via a flexible hose (72) which is between the gate valve (34) and the pressure feed connection (26 ) connected. 5. Low-pressure casting device according to one of claims 2 to 4, characterized in that the Cylinder (58) is provided with a return device (ballast weight 74) which brings it into a position of equilibrium, in which the partition (62) is vertical. 6. Low-pressure casting device according to one of claims 1 to 5, characterized in that the The flow regulator (30) for the inert gas is a flow regulator acting as a pressure reducing valve. 509b / * b '/ 0872